TWI787928B - optic fibre cable - Google Patents

Abstract

The present invention is characterized in that: in the optical fiber cable, a plurality of optical fibers with geometric microbending loss characteristics F _{μBL_G} and optical microbending loss characteristics F _{μBL_Δβ are} accommodated in the inner space of the sheath, and the void ratio of the inner space is used When the cable characteristic Dc of the optical fiber cable is defined by a and the number of optical fibers accommodated in the inner space b, the microbending loss characteristic factor F _{μBL_G△β} (Pa ^-1 .m ^-2.5 .rad ^-8 ) is 1.2×10 ^-9 or less.

F _{μBL_G△β} - F _{μBL_G} × F _{μBL_△β} × Dc

Description

optic fibre cable

The present invention relates to an optical fiber cable.

In recent years, due to the maturity of Fiber To The Home (FTTH) services or the popularization of mobile terminals, the expansion of the use of cloud services, and the increase in video traffic, the communication infrastructure constructed by optical fiber cables traffic is increasing. Therefore, there is a need to build communication infrastructure more economically and efficiently than ever before. Against such a background, there is a demand to increase the number of installed cores or the installed density of optical fibers installed in optical fiber cables. In addition, in general, in an optical fiber cable, a plurality of optical fibers are housed inside a sheath which is a tubular resin member.

As a method of increasing the number of mounted fibers or the mounting density of optical fibers housed inside the sheath, it is conceivable to reduce the diameter of the optical fibers. However, in this case, the optical fiber becomes susceptible to lateral pressure, which may increase microbend loss (microbend loss). The aforementioned microbend loss is optical loss caused by the axis of the optical fiber being slightly bent, so-called microbending. . In the following Patent Document 1, it is described that the coating thickness of the optical fiber is reduced by adjusting the elastic coefficient and glass transition point of the coating of the optical fiber. Microbending loss can be suppressed.

Patent Document 1: Japanese Patent Application Publication No. 2012-508395

Summary of the invention

However, when the optical fiber cable is exposed to a low temperature environment, the sheath shrinks at low temperature, and the optical fiber is bent by being pressed by the shrinking sheath at low temperature. As a result, microbending loss occurs in the optical fiber, and the transmission loss of the optical fiber cable tends to increase. Especially in the case of using the optical fiber described in Patent Document 1 to form an optical fiber cable In some cases, since each optical fiber is thinner than ordinary optical fibers, it is considered that it is easy to bend due to pressure from the sheath, and it is easy to increase transmission loss.

Accordingly, an object of the present invention is to provide an optical fiber cable capable of suppressing an increase in transmission loss in a low-temperature environment.

In order to achieve the above object, the present invention is an optical fiber cable comprising: a plurality of optical fibers; A clad of the core; a main coating layer covering the clad; and a sub-coating layer covering the main clad layer, and the optical fiber cable is characterized in that the optical fiber has a bending rigidity of the glass part set to H _f (Pa.m ⁴ ), let the deformation resistance of the aforementioned sub-coating layer be D ₀ (Pa), let the bending rigidity of the aforementioned sub-coating layer be H ₀ (Pa.m ⁴ ), let the Yang Let the Young's modulus of the above-mentioned main coating layer be E _g (GPa), let the Young's modulus of the above-mentioned main coating layer be E _p (MPa), let the Young's modulus of the aforementioned sub-coating layer be E _s (MPa), and let the outer surface of the glass part _{Let the radius of the outer peripheral surface of the above-mentioned main coating layer be Rp (} μm), let the radius of the outer peripheral surface of the aforementioned sub-coating layer be R _s (μm), and let the radius of the outer peripheral surface of the aforementioned main coating layer be R s (μm). When the thickness of the above-mentioned sub-coating layer is set to t _p (μm) and the thickness of the aforementioned sub-coating layer is set to t _s (μm), there are

The geometric microbending loss characteristic F _{μBL_G} (Pa ^-1 .m ^-10.5 ) of the aforementioned optical fiber is represented, and the difference between the propagation constant of the aforementioned optical fiber in the waveguide mode and the propagation constant in the radiation mode that will propagate through the aforementioned optical fiber is set In the case of propagation constant difference △β(rad/m), with

The optical micro-bending loss characteristic F _{μBL_Δβ} (1/(rad/m) ⁸ ) of the aforementioned optical fiber represented, when using the porosity a of the aforementioned internal space and the number of cores b of the aforementioned optical fiber accommodated in the aforementioned internal space, When the cable characteristic Dc of the aforementioned optical fiber cable is specified by the following formula, Dc = (0.5- a ) ² / b

The microbending loss characteristic factor F _{μBL_GΔβ} (Pa ^-1 .m ^-2.5 .rad ^-8 ) represented by the following formula has a value of 1.2×10 ^-9 or less.

F _{μBL_G△β} = F _{μBL_G} × F _{μBL_△β} × Dc

Such as Non-Patent Document 1 (J. Baldauf, et al., "Relationship of Mechanical Characteristics of Dual Coated Single Mode Optical Fibers and Microbending Loss," IEICE Trans. Commun., vol. E76-B, No.4, 1993.) , Non-Patent Document 2 (K.Petermann, et al., "Upper and Lower Limits for the Microbending Loss in Arbitrary Single-Mode Fibers," J.Lightwave technology, vol.LT-4, no.1, pp.2- 7, 1986.), non-patent literature 3 (Dayue et al., "Optical Fiber", Ohmsha, Ltd., pp.235-239, 1989.) and non-patent literature 4 (P.Sillard, et al., "Micro- Bend Losses of Trench-Assisted Single-Mode Fibers, "ECOC2010, We.8.F.3, 2010.) records that the micro-bend loss of the fiber tends to be affected by both the geometry and optical properties of the fiber.

Here, the geometry of the optical fiber is a parameter related to the structure of the optical fiber. In the present invention, it refers to the bending rigidity H _f of the glass part in the optical fiber, the deformation resistance D ₀ of the sub-coating layer, and the bending rigidity of the sub-coating layer. H ₀ , Young's modulus E _g of the glass part, Young's modulus E _p of the main coating layer, Young's modulus E _s of the sub-coating layer, outer diameter d _f of the glass part (diameter of the glass part), radius of the glass part R _g , radius R _p of the main coating layer, radius R _s of the sub coating layer, thickness t _p of the main coating layer, and thickness t _s of the sub coating layer.

Also, according to the above-mentioned Non-Patent Documents 2 to 4, the microbend loss is considered to be a phenomenon caused by modal coupling in which a waveguide mode propagating through an optical fiber is coupled with a radiation mode. This modal coupling It is considered that the fusion occurs due to the above-mentioned microbending, and it is generally considered that the difference between the propagation constant in the waveguide mode and the propagation constant in the radiation mode of the light propagating through the optical fiber is the difference in propagation constant (Δβ) to decide. The above-mentioned optical characteristic of the optical fiber is a parameter related to the characteristic of light propagating through the optical fiber, and means the above-mentioned propagation constant difference Δβ (rad/m) in the present invention.

Also, as mentioned above, when the optical fiber cable is exposed to a low temperature environment, the optical fiber bends to generate micro-bending loss, and the transmission loss tends to increase. Therefore, in an optical fiber cable, in consideration of such an increase in transmission loss, it may be required to reduce the increase in transmission loss to 0.15 dB/km or less based on the normal temperature at -40°C. In addition, such an increase in transmission loss is sometimes referred to as an increase in loss in a temperature characteristic test.

The inventor of the present case has conducted incisive research on the above-mentioned transmission loss of the optical fiber cable. As a result, the inventors of the present invention have found that the value of the microbending loss characteristic factor F _{μBL_GΔβ} represented by the above formula and the value of the increase in loss in the temperature characteristic test are approximately proportional to a positive slope.

Further, the inventors of the present invention have found that when the value of the microbending loss characteristic factor is 1.2×10 ^-9 , the temperature characteristic test loss increase value is slightly smaller than 0.15 dB/km. As mentioned above, the value of the characteristic factor of the microbending loss and the value of the increase in loss in the temperature characteristic test are approximately in a proportional relationship with a positive slope. Therefore, by setting the value of the microbending loss characteristic factor of the optical fiber cable to 1.2×10 ^-9 or less, the increase in transmission loss can be suppressed in a low-temperature environment of -40°C so that the increase in transmission loss becomes 0.15dB/ km below. As such, according to this optical fiber cable, an increase in transmission loss can be suppressed in a low-temperature environment.

Further, it is preferable that the microbending loss characteristic factor F _{μBL_GΔβ} (Pa ⁻¹ .m ^−2.5 .rad ⁻⁸ ) has a value of 9.9×10 ⁻¹⁰ or less.

By setting the value of the microbending loss characteristic factor F _{μBL_G△β} (Pa ^-1 .m ^-2.5 .rad ^-8 ) below 9.9×10 ^-10 , the increase in transmission loss, that is, the increase in temperature characteristic test loss Set the value of 0.12dB/km or less.

Further, it is more desirable that the microbending loss characteristic factor F _{μBL_GΔβ} (Pa ⁻¹ .m ^−2.5 .rad ⁻⁸ ) has a value of 7.9×10 ⁻¹⁰ or less.

By setting the value of the microbend loss characteristic factor F _{μBL_G△β} (Pa ^-1 .m ^-2.5 .rad ^-8 ) below 7.9×10-10, the increase in transmission loss, that is, the increase in temperature characteristic test loss Set the value of 0.10dB/km or less.

As described above, according to the present invention, it is possible to provide an optical fiber cable capable of suppressing an increase in transmission loss in a low-temperature environment.

1: Fiber optic cable

3: Sheath

3S: Internal space

4: Core wire

4A: Joining

4B: Single core

6: Tension body

10: Optical fiber

11: Nuclei

12: fiber shell

13: Glass department

14: Main coating layer

15: Sub-coating layer

L: Straight line

d _f : outer diameter

R _g , R _p , R _s : radius

t,t _p ,t _s :thickness

Fig. 1 is a diagram schematically showing a cross-sectional structure perpendicular to the longitudinal direction of an optical fiber cable according to an embodiment of the present invention.

Fig. 2 is a perspective view schematically showing an example of an optical fiber ribbon included in the optical fiber cable shown in Fig. 1 .

3 is a diagram schematically showing a cross-sectional structure perpendicular to the longitudinal direction of an optical fiber included in the optical fiber ribbon shown in FIG. 2 .

Fig. 4 is a graph showing the relationship between the value of microbending loss characteristic factor and the amount of loss increase in a temperature characteristic test in an optical fiber cable.

form for carrying out the invention

Hereinafter, the form of the optical fiber cable used for implementing this invention is illustrated together with an attached drawing. The embodiments illustrated below are to facilitate the understanding of the present invention, and are not intended to limit the interpretation of the present invention. The present invention can be changed and improved from the following embodiments without departing from the gist. In addition, in this specification, the size of each member may be displayed exaggeratedly for easy understanding.

FIG. 1 is a diagram schematically showing a cross-sectional structure perpendicular to the longitudinal direction of an optical fiber cable 1 according to an embodiment. As shown in Figure 1, an optical fiber cable 1 is provided with a sheath 3, a plurality of ribbon core wires 4 and a tensile body 6. as the main composition.

The sheath 3 is a tubular member formed of thermoplastic resin such as polyethylene. In the inner space 3S surrounded by the sheath 3, a plurality of tape core wires 4 are accommodated. In this way, the optical fiber cable 1 of the present embodiment is a so-called ultra-high density cable (UHDC: Ultra-High Density Cable) in which a plurality of ribbon core wires 4 are closely accommodated in the inner space 3S of the sheath 3 . In this embodiment, the plurality of tape core wires 4 have the same configuration.

In this embodiment, a pair of tension members 6 are embedded in the thick portion of the sheath 3 . In the cross-sectional view of FIG. 1 , the tensile members 6 are arranged at positions facing each other across the center of the optical fiber cable 1 . With such a tension member 6, when tension acts on the longitudinal direction of the core wire 4, the core wire 4 can be suppressed from being stretched excessively. In addition, the position and number of the tension body 6 are not limited to this example, and the tension body 6 may not be provided.

FIG. 2 is a perspective view schematically showing an example of the cored wire 4 . As shown in FIG. 2, the cored wire 4 of this embodiment is a so-called intermittent bonding type. In the ribbon core 4 of this embodiment, a plurality of optical fibers 10 are arranged in a direction perpendicular to the longitudinal direction, and the arranged optical fibers 10 are bonded to each other. In the example of FIG. 2 , the number of cores of the optical fiber 10 constituting the tape core 4 is twelve. In addition, the number of cores of the optical fiber 10 constituting the cored wire 4 is not limited to 12 cores, and may be more or less than 12 cores. Also, the cored wire 4 is not limited to the intermittent bonding type.

The tape core 4 includes a bonding portion 4A and a single core portion 4B. The bonding portion 4A is formed of, for example, UV curable resin or thermosetting resin, and is bonded to adjacent optical fibers 10 to connect these optical fibers 10 to each other. The joint portion 4A is intermittently provided at a constant pitch along the longitudinal direction. The single-core portion 4B is a portion located between the bonding portions 4A, and is a portion where the optical fibers 10 are not bonded to each other. With this configuration, the tape core wire 4 can be easily deformed, and can be twisted or bundled into a substantially cylindrical shape, for example. FIG. 1 schematically shows a state in which each cored wire 4 is bundled into a substantially cylindrical shape.

However, when the volume of the inner space 3S of the sheath 3 is set as A, and the When the sum of the volumes of various members of the space 3S is B, the porosity a of the internal space 3S can be determined as follows.

a=(A-B)/A

The smaller the porosity a, the tighter the optical fibers 10 are arranged. In this embodiment, as shown in FIG. 1 , the members housed in the internal space 3S are a plurality of strip core wires 4 . Therefore, the value of B described above corresponds to the sum of the volumes of the plurality of tape core wires 4 in the internal space 3S. In addition, in the present embodiment, as described above, since the plurality of tape core wires 4 have the same configuration, they have substantially the same volume. Therefore, when V is the volume and c is the number of cored wires 4 accommodated in the internal space 3S, the value of B above can be represented by c×V.

In addition, the value of the said porosity a is not specifically limited. However, when the porosity a is too small, the density of the optical fibers becomes too large, and the lateral pressure on the adjacent optical fibers 10 increases, which may lead to an increase in the microbending loss. Therefore, in consideration of increasing the number of optical fibers 10 in the optical fiber cable 1 and suppressing the above-mentioned lateral pressure, the porosity a may be, for example, not less than 0.31 and not more than 0.42.

FIG. 3 is a diagram showing a cross-sectional structure perpendicular to the longitudinal direction of the optical fiber 10 constituting the ribbon core 4 . The optical fiber 10 of this embodiment is a single-mode optical fiber. As shown in FIG. 3 , the optical fiber 10 mainly includes a core 11 , a sheath 12 surrounding the core 11 without gaps, a main cladding layer 14 covering the sheath 12 , and a sub-cladding layer 15 covering the main cladding layer 14 . In the optical fiber 10 , the shell 12 has a lower refractive index than the core 11 .

The core 11 may be formed of pure quartz to which no dopant is added, or may be formed of quartz to which germanium (Ge) or the like is added as a dopant to increase the refractive index.

As mentioned above, the sheath 12 has a lower refractive index than the core 11 . For example, when the core 11 is formed of pure quartz, the shell 12 may be formed of quartz to which fluorine (F) or boron (B) or the like is added as a dopant to lower the refractive index, and when the core When 11 is made of quartz doped with germanium (Ge), which increases the refractive index, etc., the shell 12 may be made of pure quartz without dopant added. In addition, the shell 12 may also be formed of quartz added with chlorine (Cl2). In addition, the fiber shell 12 may be a single layer, or may be composed of a plurality of layers with different refractive indices, or may be a hole-assisted type.

Thus, both the core 11 and the shell 12 are formed of quartz (glass). Therefore, if the core 11 and the shell 12 are collectively referred to as the glass portion 13 , the glass portion 13 includes the core 11 and the shell 12 , and the glass portion 13 is covered by the main cladding layer 14 . In addition, the glass part 13 is also called a bare fiber. The outer diameter (diameter) _df of the glass portion 13 of this embodiment is smaller than the outer diameter of the glass portion of a general optical fiber, which is about 125 μm, and may be, for example, 80 μm or more and 90 μm or less.

The main coating layer 14 is formed of, for example, an ultraviolet curable resin or a thermosetting resin, and is formed on the outside of the glass portion 13 with a thickness t _p (μm). In the present embodiment, the Young's modulus E _g of the main covering layer 14 is lower than the Young's modulus E _s of the sub covering layer 15 . By setting the main coating layer 14 in direct contact with the glass portion to have a low Young's modulus, the main coating layer 14 functions as a buffer material, and the external force acting on the glass portion 13 can be reduced. In addition, when the radius of the outer peripheral surface of the main coating layer 14 is R _p (μm), the outer diameter of the main coating layer 14 is represented by 2R _p , and when the radius of the glass portion (d _f ×1/ 2) When R _g (μm) is used, the aforementioned thickness t _p of the main coating layer 14 is represented by the following formula.

t _p =R _p -R _g

In the present embodiment, the sub-coating layer 15 is a layer forming the outermost layer of the optical fiber 10, and is formed of, for example, an ultraviolet curable resin or a thermosetting resin different from the resin forming the main coating layer 14, and has a thickness t _s (μm) is formed outside the main coating layer 14 . For example, when the main coating layer 14 is formed of an ultraviolet curable resin, the sub coating layer 15 may be formed of an ultraviolet curable resin different from the ultraviolet curable resin forming the main coating layer 14, and when the main coating layer 14 is formed of a thermosetting resin When formed, the sub-coating layer 15 may be formed of a thermosetting resin different from that of the main coating layer 14 . In the present embodiment, the Young's modulus E _s of the sub-coating layer 15 is higher than the Young's modulus E _g of the main coating layer 14 . By setting the sub-coating layer 15 forming the outermost layer of the optical fiber 10 to have a high Young's modulus in this way, the glass portion 13 can be properly protected from external force. In addition, when the radius of the outer peripheral surface of the sub-cladding layer 15 is R _s , the outer diameter of the sub-cladding layer 15, that is, the outer diameter of the optical fiber 10 is represented by 2R _s , and the above-mentioned thickness t of the sub-cladding layer 15 is _s is represented by the following formula.

t _s =R _s -R _p

In addition, the outer diameter of the optical fiber used in the optical fiber cable is generally about 240 μm to about 250 μm. However, in this embodiment, the outer diameter of the sub-coating layer 15 may be, for example, not less than 150 μm and not more than 161 μm.

Also, if the sum of the thickness t _p of the main coating layer 14 and the thickness t _s of the sub coating layer 15 is defined as the coating thickness t, the coating thickness of an optical fiber used in an optical fiber cable is generally about 60 μm. However, in this embodiment, the coating thickness t of the optical fiber 10 may be, for example, not less than 35.0 μm and not more than 37.5 μm.

As described above, in the inner space 3S of the sheath 3 of the optical fiber cable 1, the ribbon core 4 obtained by bundling 12 thin-diameter optical fibers 10 is tightly accommodated. In this way, the optical fiber cable 1 including, for example, 288 cores, 1728 cores, or more than 2000 cores of optical fibers can be configured. In addition, since the optical fiber 10 of the present embodiment has been reduced in diameter as described above, the size of the ribbon 4 can be made smaller than that of a general ribbon. Therefore, the number of optical fibers accommodated in the inner space 3S of the sheath 3 can be effectively increased. Alternatively, by accommodating the small-sized ribbon core wire 4 in the internal space 3S in this way, the size of the optical fiber cable 1 can be reduced.

When the optical fiber cable is exposed to a low temperature environment such as -40° C., the sheath will shrink at low temperature, and the optical fiber will be bent by being pressed by the low temperature shrinkable sheath. As a result, microbending loss occurs in the optical fiber, and the transmission loss of the optical fiber cable tends to increase. In particular, since the reduced diameter optical fiber is thinner than ordinary optical fibers, it is considered that it is easy to bend due to pressure from the sheath. Therefore, it is considered that when the reduced-diameter optical fiber is exposed to a low-temperature environment, the increase in transmission loss becomes larger than that of a normal optical fiber. Also, in general, the amount of shrinkage of the resin forming the sheath tends to increase as the temperature decreases. Therefore, it is considered that the lower the environment in which the optical fiber cable is used, the greater the pressure received by the optical fiber from the sheath, and as a result, the greater the increase in the transmission loss of the optical fiber cable.

However, the optical fiber cable 1 of the present embodiment is formed so that the value of the microbending loss characteristic factor F _{μBL_GΔβ} (Pa ^-1 .m ^-2.5 .rad ^-8 ), which will be described later, becomes 1.2×10 ^-9 or less. Therefore, even in the case where the optical fiber cable 1 is exposed to a low-temperature environment such as -40° C., an increase in transmission loss can be suppressed. The reason for this will be described in detail below.

As described in the above-mentioned Non-Patent Documents 1 to 4, the microbending loss of an optical fiber tends to be affected by both the geometry and optical characteristics of the optical fiber.

The geometry of the optical fiber is a parameter related to the structure of the optical fiber. In this embodiment, it refers to the bending rigidity H _f of the glass part in the optical fiber, the deformation resistance D ₀ of the sub-coating layer, and the bending rigidity H ₀ of the sub-coating layer. , Young's modulus E _g of the glass part, Young's modulus E _p of the main coating layer, Young's modulus E _s of the sub-coating layer, outer diameter d _f of the glass part (diameter of the glass part), radius R _g of the glass part , the radius R _p of the main coating layer, the radius R _s of the sub coating layer, the thickness t _p of the main coating layer, and the thickness t _s of the sub coating layer.

Also, according to the above-mentioned Non-Patent Documents 2 to 4, the microbend loss is considered to be a phenomenon caused by modal coupling in which a waveguide mode propagating through an optical fiber is coupled with a radiation mode. This waveguide mode is set as, for example, the LP01 mode. Such modal coupling is generally considered to occur when the axis of the fiber is slightly bent, the so-called microbend, and is considered to be caused by the difference between the propagation constant in the waveguide mode and the propagation constant in the radiation mode, namely the propagation Constant difference (△β) to determine. The above-mentioned optical characteristic of the optical fiber is a parameter related to the characteristic of light propagating through the optical fiber, and means the above-mentioned propagation constant difference Δβ (rad/m) in the present invention.

Also, as mentioned above, when the optical fiber cable is exposed to a low-temperature environment, micro-bending loss occurs in the optical fiber, and the transmission loss tends to increase. Therefore, in an optical fiber cable, in consideration of such an increase in transmission loss, it may be required to reduce the increase in transmission loss to 0.15 dB/km or less based on the normal temperature at -40°C. This increase in transmission loss can be obtained by the cable temperature characteristic test specified in GR-20, Issue 4, July 2013 "Generic Requirements for Optical Fiber and Optical Fiber Cable", and is sometimes called temperature characteristic Test loss increase.

The inventor of the present case has conducted incisive research on the above-mentioned transmission loss of the optical fiber cable. As a result, the inventors of the present invention based on the following formula (1) using parameters related to the above geometry

The geometrical microbending loss characteristic F _{μBL_G} of the optical fiber 10 represented, using the parameters related to the above-mentioned optical characteristics according to the following formula (2)

The optical microbending loss characteristic F _{μBL_Δβ} of the optical fiber 10 shown, the number of cores b of the optical fiber 10 accommodated in the inner space 3S of the sheath 3 using the above-mentioned porosity a and the following formula (3)

Dc =(0.5- a ) ² / b ‧‧‧(3)

The cable characteristic Dc of the specified optical fiber cable 1 was found to be expressed by the following formula (4)

F _{μBL_G△β} = F _{μBL_G} × F _{μBL_△β} × Dc ‧‧‧(4)

The value of micro-bending loss characteristic factor F _{μBL_G△β} and the value of temperature characteristic test loss increase are roughly in a proportional relationship with a positive slope.

In addition, according to Non-Patent Document 5 (K.Kobayashi, et al., "Study of Microbending loss in thin coated fibers and fiber ribbons," IWCS, pp.386-392, 1993.), the constant in the above formula (1) A typical value of μ is "3". Therefore, the above-mentioned formula (1) becomes the following formula (5).

Also, according to the above-mentioned Non-Patent Document 2 and Non-Patent Document 6 (C.D.Hussey, et al., "Characterization and design of single-mode optical fibers," Optical and Quantum Electronics, vol.14, no.4, pp.347- 358,1982.), the typical value of the constant p in the above formula (2) is "4". Therefore, the above-mentioned formula (2) becomes the following formula (6).

Further, the inventors of the present invention have found that when the value of the microbending loss characteristic factor is 1.2×10 ⁻⁹ , the increase in loss in the temperature characteristic test becomes a value slightly smaller than 0.15 dB/km. As mentioned above, the value of the characteristic factor of the microbending loss and the value of the increase in loss in the temperature characteristic test are approximately in a proportional relationship with a positive slope. Therefore, by setting the value of the microbending loss characteristic factor of the optical fiber to 1.2×10 ^-9 or less, the increase in transmission loss can be suppressed in a low temperature environment of -40°C so that the increase in transmission loss becomes 0.15dB/km the following.

Next, when the value of the microbending loss characteristic factor is 1.2×10 ^-9 , the temperature characteristic test loss increase value is slightly smaller than 0.15 dB/km.

The inventors of the present application conducted the following experiment in order to verify the relationship between the value of the microbending loss characteristic factor F _{μBL_GΔβ} and the value of the increase in loss in the temperature characteristic test. In addition, the aspect which implements this invention is not limited to this experiment.

The inventor prepared optical fiber cables of samples 1-21. Samples 1 to 21 are all the so-called narrow-diameter high-density cables in which the cored wire 4 including the 12-core optical fiber 10 shown in FIG. 2 is accommodated in the above-mentioned internal space 3S. The parameter specifications of samples 1 to 21 are shown in Tables 1 to 5 below. In Tables 1 to 5, parameters other than porosity, number of cores, microbending loss characteristic factor F _{μBL_G△β} , and temperature characteristic test loss increase are to show the specifications of the plurality of optical fibers that constitute samples 1 to 21. parameter. For example, the optical fiber cable of sample 1 shown in Table 1 has 288-core optical fibers with the same specifications, and has 24 (288/12) ribbon core wires 4 . Also, for example, the optical fiber cable of sample 12 shown in Table 3 has 1728 optical fibers with the same specification, and has 144 (1728/12) ribbon cores 4 . In addition, the sheaths 3 of the samples 1 to 21 have the same configuration.

Among the parameters showing the various specifications of the optical fiber, the modal field diameter (MFD), cut-off wave The length, MAC value, macrobend loss, and propagation constant difference are as follows.

The modal field diameter is the modal field diameter of light in the LP01 mode when light with a wavelength of 1310 nm propagates into the optical fiber. The modal field diameter is represented by the Petermann II definition formula (the following formula (7)) in ITU-T recommendation G.650.1. Here, E(r) represents the electric field intensity at the point where the distance r from the central axis of the optical fiber becomes.

The cutoff wavelength is the minimum wavelength that shows sufficient attenuation of the higher order modes. This higher order mode refers to eg the LP11 mode. Specifically, it is the minimum wavelength at which the high-order mode loss becomes 19.3 dB. The cutoff wavelength includes a fiber cutoff wavelength and a cable cutoff wavelength, and can be measured by, for example, the measurement method described in ITU-T Recommendation G.650. The cable cutoff wavelengths are listed in Tables 1 to 5. Also, the MAC value is the ratio of the modal field diameter of light with a wavelength of 1310nm to the cable cut-off wavelength, and can be defined as 2w/λ _cc when the modal field diameter is 2w and the cable cut-off wavelength is λ _cc . Also, the large bending loss is the bending loss caused by the light having a wavelength of 1625 nm propagating in the bent portion when the optical fiber is bent with a radius of 10 mm. "/turn" in the unit of large bending loss means "per one bend of the optical fiber". Also, the propagation constant difference is the difference between the propagation constant in the waveguide mode of light with a wavelength of 1550nm and the propagation constant in the emission mode of light with a wavelength of 1550nm. The difference between the propagation constant and the propagation constant in the LP11 mode. The propagation constant is based on the refractive index distribution of the fiber being tried, using non-patent literature 7 (K.Saitoh and M.Koshiba, "Full-Vectorial Imaginary-Distance Beam Propagation Method Based on a Finite Element Scheme: Application to Photonic Crystal Fibers, "IEEE J.Quant.Elect.vol.38,pp.927-933,2002.) The two-dimensional finite element method recorded.

The values of microbending loss characteristic factors F _{μBL_G△β} of the optical fiber cables of samples 1-21 are obtained by substituting the values of the parameters recorded in Tables 1-5 into formulas (3), (4), (5) and (6) to find out.

As mentioned above, the temperature characteristic test loss increase of the optical fiber cables of samples 1~21 is determined by the cable temperature characteristic test specified in GR-20, Issue 4, July 2013 "Generic Requirements for Optical Fiber and Optical Fiber Cable" Find out. Specifically, a cable with a total length of 1 km is wound on a drum, and after putting the drum into a constant temperature tank at room temperature, one end and the other end of the cable are taken out from the constant temperature tank for 3 m each, and connected to an OTDR (Optical Time Domain Reflectometry) instrument, Optical Time Domain Reflectometer). As the above-mentioned drum, a drum having a drum diameter in which the overlapping of wound cables becomes 7 layers or less was selected. In addition, it is known that the diameter of the drum hardly affects the measured value in the above-mentioned cable temperature characteristic test. Therefore, it is also possible to use rollers having different roller diameters than those described above. Next, the value of the transmission loss of light with a wavelength of 1625 nm propagating through the above cable was measured in a state where the thermostat was at normal temperature. Then, spend more than 1.5 hours to lower the temperature of the constant temperature bath, after confirming that the temperature has reached -40°C, and keep the temperature at -40°C for 12 hours, measure the intensity of the light with a wavelength of 1625nm propagating in the above-mentioned cable. The value of the transmission loss. The difference between the value of this transmission loss and the value of transmission loss measured at the above normal temperature was calculated|required, and this difference was made into the temperature characteristic test loss increase amount.

The inventors of this case plotted sample 1 on the coordinates where the value of microbending loss characteristic factor F _{μBL_G△β} is on the horizontal axis (X axis) and the value of temperature characteristic test loss increase is on the vertical axis (Y axis). ~21 The value of micro-bending loss characteristic factor F _{μBL_G△β} and the value of temperature characteristic test loss increase. As a result, a scatter diagram as shown in Fig. 4 was obtained. After obtaining the function from this scattergram using the least square method, a linear function having a positive slope represented by the following formula (8) can be obtained. Also, the correlation coefficient of the data in Fig. 4 was 87% or more.

Y =10 ⁸ X +0.021‧‧‧(8)

In addition, in FIG. 4, this linear function is shown as a straight line L. As such, it can be seen that the value of the microbending loss characteristic factor F _{μBL_G△β} has a high correlation with the value of the temperature characteristic test loss increase, specifically, the value of the microbending loss characteristic factor F _{μBL_G△β} The value of the increase in loss in the characteristic test is a proportional relationship with a substantially positive slope.

As mentioned above, in optical fiber cables, it tends to be required to reduce the increase in transmission loss to 0.15 dB/km or less based on the normal temperature at -40°C. Therefore, after calculating the value of the microbending loss characteristic factor F _{μBL_G△β} (Pa ^-1 .m ^-2.5 .rad ^-8 ) according to formula (8), it can be known that when the value is 1.2×10 ^-9 In this case, the increase in loss in the temperature characteristic test becomes a value slightly smaller than 0.15dB/km.

Therefore, according to the optical fiber cable 1 of the above-mentioned embodiment in which the value of the characteristic factor F _{μBL_GΔβ} (Pa ^-1 .m ^-2.5 .rad ^-8 ) of the microbending loss is 1.2×10 ^-9 or less, it can be used at a low temperature of -40°C. The increase in transmission loss is suppressed under the environment so that the increase in transmission loss becomes 0.15 dB/km or less.

In addition, as shown in Fig. 4, it can be seen that as long as the value of the microbending loss characteristic factor F _{μBL_G△β} (Pa ^-1 .m ^-2.5 .rad ^-8 ) is 9.9×10 ^-10 or less, the transmission loss can be reduced to The increase amount, that is, the value of the temperature characteristic test loss increase amount is set to be 0.12 dB/km or less. In addition, it can be seen that as long as the value of the microbending loss characteristic factor F _{μBL_G△β} (Pa ^-1 .m ^-2.5 .rad ^-8 ) is 7.9×10 ^-10 or less, the increase in transmission loss, that is, the temperature characteristic test The value of the loss increase amount is set to be 0.10 dB/km or less.

As mentioned above, although this invention was demonstrated using the said embodiment as an example, this invention is not limited to this.

For example, in the above-mentioned embodiments, an example in which the sub-coating layer is the outermost layer of the optical fiber has been described. However, even when the colored layer is provided as the third coating layer on the outer periphery of the sub-coating layer, as long as the Young's modulus of the colored layer is not significantly different from that of the sub-coating layer, the sub-layer and the colored layer may be included. It is applied to the present invention as the second covering layer, that is, the sub-covering layer.

In addition, in the above-mentioned embodiment, the example in which the optical fiber cable is configured by accommodating the ribbon core wire in the internal space 3S of the sheath 3 has been described. However, it is also possible to accommodate a plurality of single-core optical fibers in the internal space 3S to form an optical fiber cable. In an optical fiber cable composed of single-core optical fibers, each optical fiber is pressed by the sheath 3 when the sheath 3 shrinks in a low-temperature environment. However, these single-core optical fibers are not fixed to other optical fibers unlike the case of the ribbon core, so even when pressed by the sheath 3, compared with the case of the ribbon core, they can be held inside without being bound by other optical fibers. Move within 3S of space. In this way, the single-core optical fiber has a large degree of freedom of movement in the internal space 3S. Therefore, the pressure that each optical fiber receives from the sheath 3 can be reduced, so that the microbending loss of the optical fiber can be reduced. From this, it is considered that the increase in transmission loss becomes smaller compared to the case of the corded wire. On the other hand, when an optical fiber cable is formed of a ribbon, the movement of each optical fiber constituting the ribbon is constrained by the other optical fibers constituting the ribbon. This point is the same regardless of the number of cores of the optical fiber constituting the cored wire. That is, it can be considered that in the ribbon, the degree of freedom of movement of each optical fiber is substantially equal regardless of the number of cores of the optical fibers constituting the ribbon. Therefore, it is considered that when an optical fiber cable is constituted by a ribbon, even when the number of cores of the optical fibers constituting the ribbon is other than 12, the pressure that each optical fiber receives from the sheath 3 is approximately equal to that of the case of 12 cores, and The microbending losses are also approximately equal. According to this, even in the case where the optical fiber cable is constituted by ribbon cores other than 12 cores, the relationship between the value of the microbending loss characteristic factor F _{μBL_GΔβ} and the value of the increase in loss in the temperature characteristic test can be roughly expressed as Formula (8) to express. Therefore, by setting the value of the microbending loss characteristic factor F _{μBL_GΔβ} (Pa ^-1 .m ^-2.5 .rad ^-8 ) to 1.2×10 ^-9 or less, regardless of the number of cores of the optical fiber constituting the ribbon core, the The increase in transmission loss can be kept below 0.15dB/km in a low temperature environment of -40°C.

According to the present invention, it is possible to provide an optical fiber cable capable of suppressing an increase in transmission loss in a low-temperature environment, which can be used in fields such as communication infrastructure.

L: Straight line

Claims (3)

An optical fiber cable, comprising: a plurality of optical fibers; and a sheath for accommodating the plurality of the aforementioned optical fibers in an inner space, the aforementioned optical fibers comprising: a glass part, including a fiber core and a fiber shell surrounding the aforementioned fiber core; a main coating layer, covering The fiber shell; and a sub-coating layer covering the main coating layer, and the optical fiber cable is characterized in that: the bending rigidity of the glass portion of the optical fiber is H _f (Pa.m ⁴ ), and the sub-coating layer is Let the deformation resistance be D ₀ (Pa), let the bending rigidity of the sub-coating layer be H ₀ (Pa.m ⁴ ), let the Young’s modulus of the glass part be E _g (GPa), let the main coating The Young's modulus of the layer is _Ep (MPa), the Young _'s modulus of the sub-coating layer is Es (MPa), the outer diameter of the glass part is _df (μm), and the main coating layer is The radius of the outer peripheral surface is R _p (μm), the radius of the outer peripheral surface of the sub-coating layer is R _s (μm), the thickness of the main coating layer is t _p (μm), and the sub-coating layer is R s (μm). When the thickness of the layer is set to t _s (μm), it has

The geometric microbending loss characteristic F _{μBL_G} (Pa ^-1 .m ^-10.5 ) of the aforementioned optical fiber is represented, and the difference between the propagation constant of the aforementioned optical fiber in the waveguide mode and the propagation constant in the radiation mode that will propagate through the aforementioned optical fiber is set In the case of propagation constant difference △β(rad/m), with

The optical micro-bending loss characteristic F _{μBL_Δβ} (1/(rad/m) ⁸ ) of the aforementioned optical fiber represented, when using the porosity a of the aforementioned internal space and the number of cores b of the aforementioned optical fiber accommodated in the aforementioned internal space, When the cable characteristic Dc of the aforementioned optical fiber cable is defined by the following formula, Dc = (0.5- a ) ² / b The microbending loss characteristic factor F _{μBL_G△β} (Pa ^-1 . The value of m ^-2.5 .rad ^-8 ) is 1.2×10 ^-9 or less, F _{μBL_G△β} = F _{μBL_G} × F _{μBL_△β} × Dc . The optical fiber cable according to claim 1, wherein the microbending loss characteristic factor F _{μBL_GΔβ} (Pa ^-1 .m ^-2.5 .rad ^-8 ) has a value of 9.9×10 ^-10 or less. The optical fiber cable according to claim 2, wherein the microbending loss characteristic factor F _{μBL_GΔβ} (Pa ^-1 .m ^-2.5 .rad ^-8 ) has a value of 7.9×10 ^-10 or less.

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